1. Field of the Invention
The present invention relates to a continuous steam pyrolysis method, and more particularly, relates to a continuous steam pyrolysis method for pyrolyzing waste tires with the use of superheated steam.
2. Descriptions of the Related Art
Waste tires are generally recycled using two methods. The first method is the physical processing method, in which the waste tires are broken up, then the steel wires, nylon and rubber are separated, and finally the rubber is recycled in the form of raw rubber. However, as a recycled material, the recycled rubber has poor quality and is inappropriate for use as a raw material to produce tires. The recycled rubber thus obtained has a low resource utilization factor and is less economical. The other processing method incorporates a chemical process, in which the waste tires are broken up after adding an appropriate percentage of catalyst. Then, the waste tires are pyrolyzed at an appropriate temperature and an appropriate pressure to produce gaseous products, blended oils, carbon black, residuals and the like. Then, with an appropriate separating process such as a fractionating process, the byproducts with high economical value such as light oil, gasoline, kerosene, diesel oil and heavy oil may be separated from the blended oils. Recycling waste tires are, thus, more efficient.
It can be seen from the above description that the pyrolysis method for processing waste tires delivers a substantially better recycling economical benefit. Therefore, most of the related development efforts under way at present are directed to such a method. Conventional waste tire pyrolysis technologies may further be divided into two categories, namely, pyrolysis-in-batch technologies and continuous-pyrolysis technologies. For the pyrolysis-in-batch technologies, waste tires are placed into a pyrolysis furnace which is then heated to activate a pyrolysis reaction. After completing the pyrolysis reaction, the processing procedures such as cooling and depressurizing are conducted and pyro-products are taken out. Thereafter, another batch of waste tires is placed into the furnace for processing. This approach is disadvantageous in that the pyrolysis furnace must be subjected to a heating/cooling cycle for each batch and the pyrolysis reaction has to be interrupted between the individual batches, resulting in a limited processing speed and a low production throughput. Furthermore, after processing each batch, the pyrolysis furnace has to be opened to take out the reaction products before the next batch of materials to be pyrolyzed can be loaded. This makes it difficult to effectively use gases resulting from the pyrolysis reaction, and tends to cause the escaping of dust and pyro-gases. Nowadays, waste tires are mostly processed through the continuous pyrolysis method to save time and cost, increase the production throughput and decrease hazard to the environment.
There are two types of continuous pyrolysis methods, one is continuous pyrolysis-in-batch method and the other is a continuous pyrolysis method. The continuous pyrolysis-in-batch method may use the apparatus disclosed in Taiwan Patent Publication No. 366304. This apparatus uses a plurality of pyrolysis furnaces in parallel, wherein each of them is controlled independently from each other, so that these parallel pyrolysis furnaces may be operated in sequence to accomplish a continuous pyrolysis. That is, when the pyrolysis reaction carried out in each pyrolysis furnace is completed, the pyrolysis furnace is cooled down independently, and then the pyro-products are withdrawn and a next batch is loaded. However, even though the pyrolysis reaction can be performed continuously according to such a continuous pyrolysis-in-batch method, each of the furnaces is still subjected to repeated heating and cooling, as well as the loading and unloading of the furnace. Furthermore, the individual operation of each furnace makes the method more complex. Moreover, such a continuous pyrolysis apparatus that uses a plurality of pyrolysis furnaces is necessarily huge and bulky in volume, and consequently limits its use in application.
Recently, continuous pyrolysis methods capable of achieving the continuous pyrolysis objective without the need of a plurality of parallel pyrolysis furnaces have been developed. An example of such methods can be accomplished by a continuous pyrolysis apparatus disclosed in Taiwan Patent Publication No. 361356. The apparatus comprises a vertically arranged stirrer, which has a stirring rod and an auger conveyor disposed thereon to assist in stirring, preheating, pyrolyzing the waste rubber and preventing occurrence of the bridging phenomenon. However, the method carried out with the use of this pyrolysis apparatus is a dry pyrolysis method which uses a dry gas, such as an inert gas, to carry the resultant pyro-gas out. When using a dry pyrolysis method, the pyrolysis furnace may explode due to a significant amount of combustible oil gases generated during the pyrolysis which is conducted at high temperature. Moreover, sulfurous component(s) contained in waste tires will be released during the pyrolysis of the waste tires. For a conventional pyrolysis technology using an inert gas as the carrier gas, the gaseous sulfurous component(s) will lead to a high sulfur content in the resultant pyro-products according to Henry's Law, and the quality of the products is thereby lowered.
In view of the disadvantages of conventional pyrolysis methods, a pyrolysis method is provided in the present invention, which allows for continuous pyrolysis without the need of a plurality of pyrolysis furnaces and can prevent blocking and bridging in the pyrolysis furnace. Furthermore, the pyrolysis method according to the invention allows for a continuous pyrolysis reaction and eliminates the complex operational procedures of heating up or cooling down the pyrolysis apparatus. Additionally, the method according to the invention is carried out in the presence of a steam flow, so that it can reduce the likelihood of explosion caused by combustible oil gases generated in the pyrolysis furnace, reduce the potential risks of the pyrolysis apparatus, and effectively dissolve the sulfurous component(s) into the steam and then carry the sulfurous component(s) out with the steam to reduce the sulfur content in the reaction products and the potential pollution extent on the environment.